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Alkanes
12.1 Alkanes: saturated hydrocarbons that contain only single 12.4 Combustion of alkanes:
carbon-carbon bonds, used as fuels, lubricants and
chemical feedstock. Hydrocarbon + oxygen ——> carbon dioxide + water
General formula as CnH2n+1
Naming: comes from the longest chain of carbon atoms, to Gives out a large amount of heat, exothermic, the
give you the root then add the functional group suffix and longer the hydrocarbon chain the more heat that’s
any branching prefix produced.
Incomplete combustion occurs when there’s not
Properties: enough oxygen.
• non-polar because the electronegativity if hydrogen and
carbon are so similar therefore they only have van der Hydrocarbon + oxygen —> carbon monoxide + water
waals between them. (+ soot)
• Increasing boiling point as the chain length increases, Effects the atmosphere:
this is because there’s more van der waals forces between • CO, a poisonous gas
them so there’s a stringer electrostatic attraction to • NO, NO2, N2O4,
overcome. Branched alkanes, cycloalkanes have a lower • SO2, leads to acid rain
boiling point as the van der waal forces are less tightly • Particulates can cause
packed, making them weaker. • Unburnt hydrocarbons can increase smog
• insoluble because the carbon bonds are non-polar • CO2, increases the amount of greenhouse gases
therefore cannot mix
So2 can react with oxygen in the air to produce
sulphuric acid which can make acid rain..
12.2 Fractional distillation of crude oil:
SO2 + 1/2O2 + H2O ——-> H2SO4
To remove SO2 you undergo flue gas
Crude oil is a fossil fuel and therefore is non-renewable, it
desulphurisation.
contains many different compounds and different length
CaO + 2H20 + SO2 + 1/2O2 —-> CaSO42H2O
hydrocarbons.
CaCO3 + 1/2O2 + SO2 —> CaSO4 + CO2
Fractional distillation, converts crude oil into different
chained hydrocarbons by separating them based on their
Catalytic converters aim to remove as many of the
boiling points in a fractionating tower.
polluting gases as possible, uses platinum and
1. Crude oil heated in furnace
rhodium
2. Mixture passes into tower where it’s hottest at the
2CO + 2NO —-> N2 + 2CO2
bottom, coolest at the top.
3. Vapour passes up the tower via trays, condensing at
greenhouse effect-carbon dioxide creates a layer
their boiling point
around the earth in the atmosphere, the sun passes
4. Mixture of liquids piped off
through it onto the earth’s surface, normally it will
5. thick residue at the bottom of tower called bitumen can
then reflect outwards however the carbon dioxide layer
be used a chemical feedstock or for road surfacing.
keeps it in and insulates the earth. Other gases are
more effective than CO2, having a faster impact on
the environment.
12.3 Industrial cracking: carbon neutral: a process that uses the same amount
of carbon dioxide that it produces, making it better for
Shorter chains produce from fractional distillation is more the environment in theory.
economically beneficial therefore the longer chains are
cracked, broken down to give shorter chains or Alkenes.
Thermal cracking-high temperatures at 700-1200K under 12.5 Formation of Halogenoalkanes:
high pressure 7000kPa, break so one electron from the
bond goes to each carbon atom to produce free radicals. The Free radical substitution-a substitution reaction
free radical react together to produce shorter chains and between an alkane and a halogen in the presence of uv
alkenes. light, creating a chain reaction.
Produces: Alkenes mostly 1. Chlorine atoms are broken down into free radicals
Catalytic cracking-at a lower temperature 720K and a due to the uv light
lower pressure using a zeolite (silicon dioxide and Cl2 ——-> 2Cl
aluminium oxide) catalyst. 2. Cl free radical reacts with alkane to become stable,
Produces: branched alkanes, cycloalkanes and aromatic producing another free radical.
compounds Cl + CH4 ——> HCl + CH3
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